Multistage Centrifugal Compressor Bypass Passages for Lower Seal Load
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Solution Overview
Problem
In multistage centrifugal compressors, the pressure difference between fluids entering and exiting the impellers creates a high load on seals, necessitating expensive designs to manage the pressure difference and thermal gradients, which restricts design freedom.
Innovation Solution
The compressor incorporates a multistage rotor with impeller stacks, balance pistons, and independent first and second internal passages between the impeller stack and shaft body, allowing fluid to bypass through extraction and return passages to equalize pressures and reduce the load on seals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a seal is used to prevent air flow between the compression passage and return passage, then air flow is prevented, but the pressure difference increases toward the upstream side, increasing the load on the seal
Solution Approach 1:
The patent introduces an intermediary passage (the radial gap between the impeller and shaft) that allows controlled fluid communication between the compression passage and return passage. This intermediary structure mediates the pressure difference by providing a gradual pressure transition path rather than a direct seal interface, thereby reducing the load on the seal while maintaining sealing performance.
2Force
If the pressure difference across the seal is reduced, then the load on the seal decreases, but the design becomes more complex with additional internal passages
Solution Approach 1:
The radial gap between the impeller and shaft serves multiple functions simultaneously: it acts as a bearing clearance for mechanical support, a thermal conduction path for heat dissipation, and a pressure equalization passage for reducing seal load. By making this structural feature multi-functional, the patent avoids adding separate components, thereby reducing overall device complexity while achieving the desired load reduction on the seal.
3Reliability
If expensive seals are used to withstand high pressure difference, then sealing reliability improves, but cost increases and design freedom is restricted
Solution Approach 1:
The patent changes the pressure parameter distribution across the seal interface by introducing the internal passage system. This parameter change (reducing the pressure difference across the seal) allows the use of simpler, more cost-effective seal designs with greater design flexibility, while still maintaining adequate sealing reliability for the application.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the load on seals, lowers costs, and enhances design flexibility by minimizing pressure differences across the seals, thereby reducing material and design constraints.
Implementation Method 1
part of the fluid flowing through the compression passage flows to the return passage through the internal passage... equalize pressures and reduce the load on seals
Implementation Method 2
compresses fluid by centrifugal force generated when the fluid to be compressed flows in a radial direction through the impellers that are rotating
Data Source
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AI summary
A multistage centrifugal compressor includes: a compression passage through which fluid to be compressed flows; and a first internal passage and a second internal passage which are located between an impeller stack and a shaft body in a radial direction and extend in an axial direction. The first internal passage communicates with the compression passage through a first return passage and a first extraction passage. The first return passage is in connection with a first return position of the compression passage, and the first extraction passage is in connection with a first extraction position located downstream of the first return position of the compression passage. The second internal passage communicates with the compression passage through a second return passage and a second extraction passage. The second return passage is in connection with a second return position located downstream of the first extraction position of the compression passage, and the second extraction passage is in connection with a second extraction position located downstream of the second return position.